The present invention relates to a modular inlet gearbox for a gas turbine engine, and more particularly, to such a gearbox which provides improved assembly and disassembly of a gas turbine engine.
A typical gas turbine engine may include: a fan section; a compressor section; a combustor section; a high pressure turbine section; a low pressure turbine section; and an exhaust section. In the operation of such a typical gas turbine engine, controlled ignition in the combustor section is utilized to drive the high pressure turbine, low pressure turbine and fan sections in a regenerative manner. Such engines require a number of controls and accessories, including such devices as fuel pumps and fuel controls. These controls and accessories are powered through a gearing relationship to the engine. In this connection, an inlet gearbox is provided for tapping a portion of the rotational energy of the compressor and developing an inlet gearbox output. The inlet gearbox includes a horizontal gear portion, typically referred to as a horizontal bevel gear, for tapping the rotational energy of the compressor and a vertical gear portion for providing the output drive energy of the inlet gearbox. The output of the inlet gearbox is utilized to drive other control accessory gearboxes and ultimately to drive particular controls and accessories. One exemplary inlet gearbox is described in U.S. Pat. No. 3,226,987, entitled "Gear Assembly," issued Jan. 4, 1976, to W. V. McCarty.
In one form of inlet gearbox, the inlet gearbox is constructed in a controlled environment, e.g., a gearbox room, where it is also provided with an inlet gearbox horizontal bearing. The inlet gearbox, including the gearbox horizontal bearing, is then assembled as part of the gas turbine engine. In this connection, the front end of the compressor section, often referred to as the compressor stub shaft, is also provided with a rotational bearing. When such an inlet gearbox is assembled into the engine, there thus results two horizontal bearings at the gearbox-stub shaft interface. These bearings must be carefully aligned for successful engine operation. The two-bearing structure generally requires a flexible drive, e.g., spline, connection between the inlet gearbox and the front end of the compressor. It has been found that these bearings, and the flexible drive spline, often exhibit undesirable wear characteristics due to misalignment which tend to reduce engine part life.
In another form of inlet gearbox, an attempt is made to simplify the inlet gearbox by combining the functions of the previously mentioned bearings into a single bearing. In this form, the horizontal bevel gear is assembled onto the front end of the compressor section. This inlet gearbox requires substantial assembly time and effort to obtain correct bevel gear axial locations, thereby lengthening the overall assembly time of the engine.
The previously noted forms of inlet gearboxes exhibit certain undesirable characteristics. In this connection, manufacturing tolerances are such that during assembly of the engine, the inlet gearbox and associated horizontal bearing may require considerable machining and/or adjustment. Also, disassembly of conventional inlet gearboxes and the engine is often difficult and time-consuming to accomplish. In addition, the use of two horizontal bearings creates a cost and weight penalty as compared to a single horizontal bearing for rotatably supporting both the inlet gearbox and the front end of the compressor section.